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How is breast cancer staged?

After a woman is diagnosed with breast cancer, doctors will figure out whether it has spread, and if so, how far. This is called staging. The stage of a cancer helps determine how serious the cancer is and how best to treat it.

What is staging?

Staging is the process of finding out how widespread the cancer is when it is found. The stage is the most important factor in deciding how to treat the cancer and determining how successful treatment might be.

To determine the cancer’s stage after a breast cancer diagnosis, doctors must answer these questions:

Is the cancer invasive or non-invasive?

How big is the breast tumor? Has it grown into nearby areas?

Has the cancer spread to nearby lymph nodes? If so, how many are involved?

Has the cancer spread to other parts of the body?

Depending on the results of your physical exam and biopsy, you might need more tests to help determine the stage, such as a chest x-ray, mammograms of both breasts, bone scans, CT scans, MRI, and/or PET scans. Blood tests may also be done to evaluate your overall health or to check for spread to certain organs.

After looking at your test results, your doctor will tell you the stage of your cancer. The earliest stage cancers are called stage 0 (carcinoma in situ), and then range from stages I (1) through IV (4). Some of the stages are further divided into sub stages using the letters A, B, and C.

As a rule, the lower the number, the less the cancer has spread. A higher number, such as stage IV (4), means a more advanced cancer. And within a stage, an earlier letter means a lower (and often better) stage. Cancers with similar stages tend to have a similar outlook and are often treated in much the same way.

Understanding your breast cancer stage

Breast cancer is staged using the American Joint Committee on Cancer (AJCC) TNM system, which is based on:

The size of the breast tumor (T) and if it has grown into nearby areas

Whether the cancer has reached nearby lymph nodes (N)

Whether the cancer has metastasized (spread to other parts of the body) (M)

Once the T, N, and M categories for your cancer have been determined, your doctor will combine the information to find the stage of the cancer. This process is called stage grouping. Cancers with similar stages tend to have a similar outlook and are often treated in a similar way.

Stage 0

Tis, N0, M0

This is ductal carcinoma in situ (DCIS), a pre-cancer of the breast. Many consider DCIS the earliest form of breast cancer. In DCIS, cancer cells are still within a duct and have not invaded deeper into the surrounding fatty breast tissue.

Lobular carcinoma in situ (LCIS) sometimes also is classified as stage 0 breast cancer, but most oncologists believe it is not a true cancer or pre-cancer.

Paget disease of the nipple (without an underlying tumor mass) is also stage 0.

In all cases the cancer has not spread to lymph nodes or distant sites.

Stage IA

T1, N0, M0

The tumor is 2 cm (about 3/4 of an inch) or less across (T1) and has not spread to lymph nodes (N0) or distant sites (M0).

Stage IB

T0 or T1, N1mi, M0

The tumor is 2 cm or less across (or is not found) (T0 or T1) with micrometastases in 1 to 3 axillary lymph nodes (the cancer in the underarm lymph nodes is greater than 0.2mm across and/or more than 200 cells but is not larger than 2 mm)(N1mi). The cancer has not spread to distant sites (M0).

Stage IIA

T0 or T1, N1 (but not N1mi), M0:

The tumor is 2 cm or less across (or is not found) (T1 or T0) and either:

It has spread to 1 to 3 axillary (underarm) lymph nodes, with the cancer in the lymph nodes larger than 2 mm across (N1a),

OR

Tiny amounts of cancer are found in internal mammary lymph nodes (nodes near the breast bone) on sentinel lymph node biopsy (N1b),

OR

It has spread to 1 to 3 axillary lymph nodes and to internal mammary lymph nodes (found on sentinel lymph node biopsy) (N1c).

The cancer has not spread to distant sites (M0).

OR

T2, N0, M0

The tumor is larger than 2 cm but less than 5 cm (about 2 inches) across (T2) but hasn't spread to the lymph nodes (N0). The cancer has not spread to distant sites (M0).

Stage IIB

T2, N1, M0

The tumor is larger than 2 cm but less than 5 cm across (T2). It has spread to 1 to 3 axillary lymph nodes and/or tiny amounts of cancer are found in internal mammary lymph nodes on sentinel lymph node biopsy (N1). The cancer hasn't spread to distant sites (M0).

OR

T3, N0, M0

The tumor is larger than 5 cm across but does not grow into the chest wall or skin (T3). The cancer has not spread to the lymph nodes (N0) or to distant sites (M0).

Stage IIIA

T0 to T2, N2, M0

The tumor is not more than 5 cm across (or cannot be found) (T0 to T2). It has spread to 4 to 9 axillary lymph nodes, or it has enlarged the internal mammary lymph nodes (N2). The cancer hasn't spread to distant sites (M0).

OR

T3, N1 or N2, M0

The tumor is larger than 5 cm across but does not grow into the chest wall or skin (T3). It has spread to 1 to 9 axillary nodes, or to internal mammary nodes (N1 or N2). The cancer hasn't spread to distant sites (M0).

Stage IIIB

T4, N0 to N2, M0

The tumor has grown into the chest wall or skin (T4), and one of the following applies:

It has not spread to the lymph nodes (N0).

It has spread to 1 to 3 axillary lymph nodes and/or tiny amounts of cancer are found in internal mammary lymph nodes on sentinel lymph node biopsy (N1).

It has spread to 4 to 9 axillary lymph nodes, or it has enlarged the internal mammary lymph nodes (N2).

The cancer hasn't spread to distant sites (M0).

Inflammatory breast cancer is classified as T4d and is at least stage IIIB. If it has spread to many nearby lymph nodes (N3) it could be stage IIIC, and if it has spread to distant lymph nodes or organs (M1) it would be stage IV.

Stage IIIC

any T, N3, M0

The tumor is any size (or can't be found), and one of the following applies:

Cancer has spread to 10 or more axillary lymph nodes (N3).

Cancer has spread to the lymph nodes under the collar bone (infraclavicular nodes) (N3).

Cancer has spread to 4 or more axillary lymph nodes, and tiny amounts of cancer are found in internal mammary lymph nodes on sentinel lymph node biopsy (N3).

The cancer hasn't spread to distant sites (M0).

Stage IV

any T, any N, M1

The cancer can be any size (any T) and may or may not have spread to nearby lymph nodes (any N). It has spread to distant organs or to lymph nodes far from the breast (M1). The most common sites of spread are the bones, liver, brain, or lungs.

The staging system in this chart uses the pathologic stage. It is based on the results of physical exam, biopsy, imaging tests, and the results of surgery, when the breast mass and nearby lymph nodes have been looked at under a microscope. This is likely to be more accurate than clinical staging, which only takes into account the tests done before surgery.

If you have any questions about the stage of your cancer and what it might mean in your case, be sure to ask your doctor.

Details of the TNM staging system

The TNM staging system classifies cancers based on 3 areas called the T, N, and M categories:

T (primary tumor) categories

The letter T followed by a number from 0 to 4 describes the main (primary) tumor's size and spread to the skin or to the chest wall under the breast. Higher T numbers mean a larger tumor and/or wider spread to tissues near the breast.

TX: Primary tumor cannot be assessed.

T0: No evidence of primary tumor.

Tis: Carcinoma in situ (DCIS, LCIS, or Paget disease of the nipple with no associated tumor mass)

T1 (includes T1a, T1b, and T1c): Tumor is 2 cm (3/4 of an inch) or less across.

T2: Tumor is more than 2 cm but not more than 5 cm (2 inches) across.

T3: Tumor is more than 5 cm across.

T4 (includes T4a, T4b, T4c, and T4d): Tumor of any size growing into the chest wall or skin. This includes inflammatory breast cancer.

N (nearby lymph node) categories

The letter N followed by a number from 0 to 3 indicates whether the cancer has spread to lymph nodes near the breast and, if so, how many lymph nodes are affected.

Lymph node staging for breast cancer is based on how the nodes look under the microscope, and has changed as technology has evolved. Newer methods have made it possible to find smaller and smaller deposits of cancer cells, but experts haven't been sure how much these tiny deposits of cancer cells affect outlook.

It’s not yet clear how much cancer in the lymph node is needed to see a change in outlook or treatment. This is still being studied, but for now, a deposit of cancer cells must contain at least 200 cells or be at least 0.2 mm across (less than 1/100 of an inch) for it to change the N stage. An area of cancer spread that is smaller than 0.2 mm (or fewer than 200 cells) doesn't change the stage, but is recorded with abbreviations (i+ or mol+) that indicate the type of special test used to find the spread.

If the area of cancer spread is at least 0.2 mm (or 200 cells), but still not larger than 2 mm, it is called a micrometastasis (one mm is about the size of the width of a grain of rice). Micrometastases are counted only if there aren't any larger areas of cancer spread. Areas of cancer spread larger than 2 mm are known to affect outlook and do change the N stage. These larger areas are sometimes called macrometastases, but are more often just called metastases.

N0(i+): The area of cancer spread contains less than 200 cells and is smaller than 0.2 mm. The abbreviation "i+" means that a small number of cancer cells (called isolated tumor cells) were seen in routine stains or when a special type of staining technique, called immunohistochemistry, was used.

N0(mol+): Cancer cells cannot be seen in underarm lymph nodes (even using special stains), but traces of cancer cells were detected using a technique called RT-PCR. RT-PCR is a molecular test that can find very small numbers of cells. (This test is not often used for finding breast cancer cells in lymph nodes because the results do not influence treatment decisions.)

N1mi: Micrometastases (tiny areas of cancer spread) in 1 to 3 lymph nodes under the arm. The areas of cancer spread in the lymph nodes are 2 mm or less across (but at least 200 cancer cells or 0.2mm across).

N1a: Cancer has spread to 1 to 3 lymph nodes under the arm with at least one area of cancer spread greater than 2 mm across.

N1b: Cancer has spread to internal mammary lymph nodes, but this spread could only be found on sentinel lymph node biopsy (it did not cause the lymph nodes to become enlarged).

N1c: Both N1a and N1b apply.

N2: Cancer has spread to 4 to 9 lymph nodes under the arm, or cancer has enlarged the internal mammary lymph nodes (either N2a or N2b, but not both).

N2a: Cancer has spread to 4 to 9 lymph nodes under the arm, with at least one area of cancer spread larger than 2 mm.

N2b: Cancer has spread to one or more internal mammary lymph nodes, causing them to become enlarged.

N3: Any of the following:

N3a: either:

Cancer has spread to 10 or more axillary lymph nodes, with at least one area of cancer spread greater than 2mm, OR

Cancer has spread to the lymph nodes under the collar bone (infraclavicular nodes), with at least one area of cancer spread greater than 2mm.

N3b: either:

Cancer is found in at least one axillary lymph node (with at least one area of cancer spread greater than 2 mm) and has enlarged the internal mammary lymph nodes, OR

Cancer has spread to 4 or more axillary lymph nodes (with at least one area of cancer spread greater than 2 mm), and tiny amounts of cancer are found in internal mammary lymph nodes on sentinel lymph node biopsy.

N3c: Cancer has spread to the lymph nodes above the collar bone (supraclavicular nodes) with at least one area of cancer spread greater than 2mm.

M (metastasis) categories

The letter M followed by a 0 or 1 indicates whether the cancer has spread to distant organs -- for example, the lungs or bones.

MX: Distant spread (metastasis) cannot be assessed.

M0: No distant spread is found on x-rays (or other imaging tests) or by physical exam.

cM0(i+): Small numbers of cancer cells are found in blood or bone marrow (found only by special tests), or tiny areas of cancer spread (no larger than 0.2 mm) are found in lymph nodes away from the breast.

M1: Cancer has spread to distant organs (most often to the bones, lungs, brain, or liver).